Solid material heating method and apparatus



May 6, 1952 P. R. GRossMAN SOLID MATERIAL HEATING METHOD AND APPARATUSFiled May 22, 194e INVENTOR ATTORNEY d'. I. m. 5

6 w LlvM N M M pau/ l?. Grossman Patented May 6, 1952l SOLID MATERIALHEATING METHOD AND APPARATUS Paul R. Grossman, Irvington, N. J.,assigner to The Babcock & Wilcox Company, New York, N. Y., a corporationof New Jersey Application May 22, 1948, Serial No. 28,586

6 Claims. l

The present invention relates to the construction and operation offurnaces or kilns of the vertical shaft type for the high temperaturetreatment of a fluent mass or column of solid material.

In 'the commercial production of burned or vitrified materials, the rawmaterial is subjected to high temperatures for a period of time sucientto allow structural and/ or chemical changes to take place in thematerial. Advantageously such a production process is performed on acontinuous basis for heat economy and uniformity of finished product.The vitrication of ceramic particle materials is particularlyadvantageously performed on a continuous basis, and vertical shaft kilnshave been used with good heat economy in the production of this type ofproduct. Unfortunately, the uniformity of vitrified ceramic particlesproduced in known types of shaft kilns has not been satisfactory, whenthe kiln is operated under maximum heat economy conditions. At thevitriiication temperature at 1east the surface of the individual bodiesof ceramic material will be in a plastic condition, and the mass must bekept moving to prevent the formation of clusters of individual particlesor bodies of the materials. A cluster will interfere with the movementof the material through the kiln and encourage the formation of otherclusters. This condition becomes aggravated by the accumulative resultsof the cluster formation until the unit must be shut down. In anyparticular shaft kiln utilized in the vitrification of a particularmaterial there is a critical range of operating temperatures Withinwhich itis possible to complete the vitrincation of the solid materialwithout forming clusters. This critical range lies Within close limitsof maximum and minimum temperatures. Thus the problem in operation ofthe kiln is to maintain the temperature of the solid materials withinthe limits of this close range and to attain a substantially uniformmaterial temperature transversely of its direction of movement in thezone pf highest material temperature. When such an objective is attainedthe uniformity of finished product will be satisfactory. y

The general object of this invention is to provide an improved method ofand apparatus for continuously heat treating a fluent mass of solidmaterial which are particularly characterized by a substantiallycontinuous movement of the solid material through a furnace or kiln ofthe vertical shaft type wherein the solid material is heated to asubstantially uniform temperature transversely of its mass in the regionof highest temperatures. A further and more specific object is toprovide a kiln of the character described which is constructed andarranged to cause a controlled heating of a moving mass of solidmaterial under optimum time-temperature conditions to an elevatedtemperature, soaking the heated material at an elevated temperature tocomplete the desired structural and/or chemical changes therein, andsubsequently cooling the heat treated material to a ldesirable handlingtemperature before its discharge from the kiln.

The various features of novelty which characterize my invention arepointed out with particularity in the claims annexed to and forming apart of this specification. For a better understanding of the invention,its operating advantages and specific objects attained by its use,reference should be had to the accompanying drawings and descriptivematter in which I have illustrated and described a preferred embodimentof my invention.

Of the drawings:

Fig. 1 is an elevation view, partly in section, of a shaft kilnconstructed in accordance with the present invention;

Fig. 2 is an enlarged section View of a portion of the apparatus shownin Fig. 1;

Fig. 3 is a cross-section taken on the line 3--3 of Fig. 2; and

Fig. 4 is an enlarged section View of another portion of the apparatusshown in Fig. l.

While this invention in its broadest aspects is adapted for thecontinuous heat treatment of a Wide range of fluent solid materials to aWide range of temperatures, it is particularly designed and especiallyuseful for the continuous firing of a fluent mass of pellets formed ofceramic materials at a temperature of the order of 3000 F.

In the drawings I have illustrated my invention as embodied in avertical shaft kiln forthe burning or vitrification of ceramicrefractory pellets intended for use as heat transfer material in fluidheating apparatus of the general type disclosed in the co-pendingapplication of E. G. Bailey and R. M. Hardgrove, Serial No. 502,580, ledSeptember 16, 1943, now Patent No. 2,447,306. Pellets of this charactermay be formed, for example, from a plastic mixture of fused alumina, rawkaolin clay, bentonite, Water and a binder. The mix is formed intosubstantially spherical pellets having a diameter in the size range ofli-l. The pellets are dried to remove the mechanical moisture thereinand are fired at a temperature of the order of 3000 F. .to obtain thestrength, hardness, and resistance to thermal shock necessary yfor theirdescribed use. Other refractory compositions have been successfullyfired at both higher and lower temperatures in the described kiln.

In the vitrication of the ceramic pellets described, the pellets areheated to the vitrification temperature, maintained at this temperaturelong enough for the necessary structural and chemical changes to takeplace, and then advantageously cooled to a convenient handlingtemperature. A shaft kiln is an efficient apparatus for performing thisprocess, since the process can be continuous and the kiln acts as acountercurrent heat exchanger during both the heating and coolingcycles. Thus, after operating equlibrium has been reached, the heatrecovered in cooling the pellets may be used in heating the material.Theoretically the additional heat added to the heating cycle may belimited to an amount necessary to compensate for radiation losses, todrive off the chemical water in the raw n ceramic material, and tosupply the heat necessary for any endothermic reactions which may takeplace in the particular material being treated. The most eiiicientheating conditions would thus be attained with a minimum temperaturedifferential between the heat exchange materials, i. e. the solids andgases, at opposite ends of the kiln. However, a desirable uniformity offinished product cannot be attained under conditions of maximumtheoretical heat eniciency.

For the necessary uniformity of lproduct, the heating gases must beintroduced into the kiln in sufiicient volume to insure a minimumtemperature differential between the entering heating gases and thepellets initially contacted by the gases. The volume of heating gaseswill be in excess of the theoretical gas quantity. Under these flowconditions the heating gases will substantially retain their enteringtemperature during the initial penetration of the moving pellet mass.Thus the pellet mass will attain a substantially uniform'l temperaturetransversely of its direction of movement in the region 0f initialheating gas contact. It will be further understood that the temperatureof the heating gas upon entering the heating zone of the kiln willadvantageouslybe essentially equal to the desired upper temperaturelimit of the pellets.

The vertical shaft kiln of the invention ccnsists of a verticallyelongated generally cylindrical gas-tight metal casing I0 enclosing avertically elongated kiln which is functionally divided into foursuperposed zones or sections, namely; a pellet preheating section II anda heating section I2 in the upper portion, a cooling section I3 in thelower portion and an intermediate soaking section I4 therebetween. Eachfunctional section of the kiln chamber is defined by a wall of suitablerefractory material, such as an inner wall portion of high temperaturefire brick I5 and a Vprotective layer of insulating material ISinterposed between the casing IIl and the wall |5. While the heating andcooling sections vI I, I2 and I3 are of substantially the same uniformdiameter through their length, the intermediate soaking section I4 is ofreduced crosssectional area for a portion of its height, as hereinafterdescribed. The upper end of the kiln is closed by a top I1 having acentrally located heating gas outlet connected with a stack I8 which isprovidedwith a flow control damper 29. The pellets to be heat treated inthe kiln are supplied to the upper endof the chamber. section II froma.hopper or receptacle. (not shown) through a solid material inlet pipe2| inserted in lied pellets.

an opening in the top Il of the kiln. Ordinarily the mass of pelletsmaintained in the pipe 2 I, and within the receptacle, will .providesuflicient flow resistance to prevent any appreciable flow of gasestherethrough to the atmosphere. rShe sealing effect of the pellet massof course depends upon the heating gas pressure prevailing in the upperend portion of the section Il. lf desired or necessary due to operatingconditions a fluid now seal, such as a star feeder or the like, may beinserted in the inlet pipe 2| to prevent an escape of heating gasestherethrough.

The bottom of the kiln, at the lowermost portion of the chamber sectionI3, is defined by an inverted frusto-conical metal screen 22 surroundedby a reduced diameter cylindrical sectionZ of the casing Ii) which has abottom discharge opening 24 spaced below the open lower end of thescreen 22 to permit any solid material passing outwardly through thescreen to reach the outlet 24 and be discharged. The screen 22 andsection 23 cooperate to define an annular fluid inlet chamber 25therebetween to which one or more valve controlled fluid supply ducts 26are connected for the admission of a fluid under pressure. The dischargeof solid material and pellets through the outlet 24 and a discharge pipe2l is controlled by a feeder, such as a screw feeder 2B, driven by asuitable variable speed drive mechanism (not shown). Thus, with the rateof solid material flow through the shaft kiln regulated by the screw 28,the dimensions of each section of the kiln will determine the relativeperiod of time each ceramic pellet will be under reatment in eachSection of the kiln.

`As hereinafter described, a measured portion of the combustion airutilized in generating the heating fluid used in the sections il and I2is passed through the section I3 to cool the vitri- The air is preheatedby its contact with the pellets and is withdrawn from the upper endportion of the section I3 to combine with additional air and fuel toburn and form a gaseous heating fluid. The flow path of the air used forpellet cooling purposes, and the heating fluid, results in anappreciable pressure differential between the top and the bottom of thekiln. While the column of pellets within the pipe 2, and the screwfeeder 28, will tend to obstruct the ow of any gaseous fluidtherethrough from the chamber 25, the pressure of the fluid within thechamber 25 will usually be sufcient to cause some fluid flow downwardlythrough the pellets to the atmosphere. Such a fluid flow is detrimentalto the operation of the process, leading to an inaccuracy in themeasured flow of air through the section I3, and is avoided bymaintaining a balanced pressure in the pipe 21 by the use of a separatesealing fluid.

The sealing fluid, which may be compressed air, is delivered under apositive pressure, in excess cf the fluid pressure occurring in thechamber 25,-and is introduced into the pipe 2l through a pipe connection30 which is located intermediate the outlet 24 and the feed screw 28.The sealing fluid pipe connection is provided with a valve 3| which maybe manually or automatically positioned to maintain a zero differentialfluid pressure between the spaced static pressure taps 32 and 33 openingrespectively into the chamber 25 and into the pipe 21 between the outlet24 and the connection 3U. As shown in Fig. 1, the taps 32 and 33 areconnected with a water manometerr34 so that the valve 3l may be adjustedfor greater or lesser sealing fluid flow to 'maintain no flow conditionsin the pipe 21 between the connection 30 and the outlet 24, as indicatedby the pressure drop between taps 32 and 33.

The mass of pellets within the upper portion of the kiln is heated bydirect contact heat exchange with the gaseous heating fluid generated bythe combustion of a fuel within a furnace 40. The furnace is verticallyelongated, of substantially uniform circular cross-section and ishorizontally spaced from the intermediate soaking secti-on I4. Asubjacent chamber 4 I, coaxial with and substantially of the diameter ofthe furnace, is formed in the wall of the kiln and connected with thefurnace 4I) by a throat 42 of reduced cross-sectional area. The chamber4I is provided with an inlet opening in its upper end for the tangentialadmission of preheated combustion air from the upper end of the kilnsection I3 through a connecting passageway 43. As shown in Figs. 1 and4, a liquid cooled gas burner nozzle 44 extends upwardly through thebottom of the chamber 4I along the vertical axis thereof to a positiondownwardly spaced from and in axial alignment with the throat 42. A

The gas nozzle 44 is shown in Fig. 4, and consists of a cylindrical tube45 which extends upwardly through the bottom of the chamber 4I to aposition spaced below the throat 42. Beneath the chamber 4I the tube 45is conveniently bent through a radius of 90 and connected with a sourceof gaseous fuel, such as a natural or articial gas pipe line (notshown). A measured portion of the air for combustion is introduced intothe tube 45 through a valved pipe 46 and combined with the fuel gasbefore the discharge of the mixture from the burner. The remainder ofthe combustion air is obtained through the passageway 43. Since thislatter combustion air is preheated in passing through the section I3, itis necessary to provide means for cooling the burner nozzle 44. This isaccomplished by enclosing the tip portion of the burner in a closelyspaced, coaxially arranged metallic jacket 41 which is seal-welded atboth ends to the tube 45. The annular chamber 48 formed between the4tube 45 and the jacket 41 is supplied with a stream of water enteringthrough a pipe 49 and escaping through a discharge pipe 50. The pipe 5I]is connected with the the upper end of the chamber 48 and islongitudinally positioned closely adjacent a side of the tube 45 toproject through the tube wall at the 90 bend. The burner, including theassembly of tube 45 and its jacket 41, is exteriorly provided with atightly fitting flanged member 5I which engages a threaded flange 52welded to the portion of the casing It beneath the chamber 4I. Anannular gasket 53, of suitable material, is interposed between the upperend of the member 5| and the adjacent portion of the casing I0, and whenthe member 5I is tightened to compress the gasket, the burner is rigidlypositioned and 'a gas-tight joint provided between the jacket 41 and thekiln casing Ill.

The preheated combustion air entering the chamber 4I through thepassageway 43 is introduced in measured amounts into the bottom of thekiln through the duct 26. The air ascends through the kiln section I3 indirect contact countercurrent relationship with the mass of pellets,with the pellets being cooled to a convenient handling temperature whilethe air acquires a high degree of preheat. The upper end of the sectionI3 is provided with a flared enlargement in the confining refractorywall. The

kiln enlargement is partially obstructed by a circulnferential series ofspaced piers 55 resting on the wall of the kiln section I3 and forming asupport for a refractory tube member 56. The member 56 forms a reducedcross-sectional area for the movement of the pellet mass through thelower portion of the kiln section I4. Due to this restricted areasubstantially all of the combustion air ascending through the section I3is deflected through a series of ports 51 between the piers 55 into anannular chamber 58 surrounding the lower end portion of the member 56and opening into the passageway 43.

The air passing upwardly through the cooling section I3 entrains dustparticles produced :by abrasion of the pellets on the wall I5 of thekiln. The dust will tend to separate from the air within the chamber 4Idue to the cyclonic motion transmitted thereto by its tangentialentrance, with a substantial portion of the dust separating and settlingto the bottom of the chamber 4I. The preheated air mixes with thegaseous fuel and air leaving the burner 44 in passing through the throat42 into the furnace where it burns with an intense llame to produce thegaseousv heating fluid. The gaseous products of combustion leave theupper end of the furnace through a radially positioned port 60 which isin communication with an annular recess BI in the wall of the kiln. Theconstruction described insures a circumferential distribution of heatinggas flow into the mass of pellets in directions generally normal to thedirection of pellet movement.

It will be noted that the furnace 4I] is positioned with its upper andlower end portions generally in communication with the opposite ends ofthe shaft kiln soaking section I4. Since the furnace is embedded in therefractory wall of the kiln which is surrounded by the insulatingmaterial I5, an appreciable portion of the heat released therein will betransmitted inwardly by conduction and convection through theintervening refractory wall to the pellets passing through the soakingsection. This heat will tend to reduce the loss of heat from the pelletsin leaving the heating section I2, so as to permit a continulation ofthe process of pellet vitrication during the period the pellets aremoving through the soaking section.

With a flow of heating gases into the heating section of the kiln at atemperature substantially equal to the vitrication temperature of theceramic material and at a flow rate adequate to insure substantiallyequivalent pellet temperatures transversely of pellet flow, the spentheating gases would leave the upper end of the kiln at a temperatureconsiderably in excess of the entering pellet temperature. This not onlylowers the thermal efliciency of the process, but also results in thedestruction of a large portion of the entering pellets as a result ofthermal shock, where the pellets frequently explode due to the hightemperature differential between green pellets and the heating gas incontact therewith. V

In accordance with my invention, I discharge a selected portion of theheating gas from a position intermediate the heating gas inlet and theupper end of the kiln. As a result, the temperature differential betweenthe heating gas and the pellets will be extremely low at the gas inletfor desirably uniform high pellet temperatures, and the temperaturedifferential between the remaining portion of the heating gas and theentering pellets will also be desirably low at the upper end of thekiln, to avoidpellet destruction from heat shock. A low temperaturediierential between the pellets and the heating gas causes a low rate ofpellet temperaturerise, which is desirable, at theY opposite ends of.the combined sections H and l2, as hereinbefore described. These heatingconditions are attained with a high rate of pellet temperature riseintermediate the portion of the kiln between the heating gas entranceand exit. The described rates of pellet temperature rise are furthermoreobtained in a comparatively short kilnk length with an advantageouslylow pressure drop of iluid ilow and low construction costs. Similarresults might be attained in an uneconomically long shaft kiln withoutthe discharge of some of the heating gases from a position intermediatethe heating length of the kiln. Such a kiln would have a heating sectionlength many times that shown in Fig. l.

As shown in Fig. 1, a pair of horizontally disposed, vertically spacedannular chambers G2 are located in the lining I5 of the kiln atpositions intermediate the heating gas inlet Bl and the top il. Theannular chambers open into the kiln and are each provided with anindividual outlet 63 through the casing I0 in communication with theatmosphere. Each of the outlets is further provided with a i'low controlmeans, such as a valve or a refractory orifice mounted in a replaceablecap 64. operated under a positive pressure, the rate of by-pass gas iiowoutwardly through the outlets 63 can be adjusted by changing the area oforil rice opening in the cap 64. As will be hereinafter apparent, theshaft kiln is operated under generally uniform material and fluid flowconditions, and once the rate of by-pass ow of heating gases is adjustedfor optimum operating conditions the orice opening in the caps 64 willremain fixed.

rihe shaft kiln of the present invention is advantageously operatedunder stabilized conditions of solid material and iluid iiows. Since theheating gas low introduced into the lower portion of the heating sectioni2 of the kiln will be in a volume in excess of the theoretical heatingrequirement, as previously described, the air required for combustionwill also be in excess of i that required for pellet cooling purposes inthe cooling section lli. As a result, only the air neoessary for coolingpurposes will be 4passed through the section i3, and the remainingportion of the air is introduced through the pipe 45 into the burnernozzle M.. However, both portions of the combustion air are measured, sothat the proper total amount of combustion air will be combi-ned withthe gaseous fuel in the furnace Il to generate a heating fluid of thedesired temperature and composition. rThe heating fluid enters thedownwardly moving mass of pellets in generally radial directions fromthe annular chamber 6l. As heretofore described the differentialtemperature of the pellets and the heating uid in the region of initialcontact is substantially zero and with suflicient gas velocities theheating fluid penetrates the mass so that the pellet temperature at thecenter is substantially equal to the pellet temperature around thecircumference of the mass. The heating gas ascends through theinterstices of the pellet mass with the pellets and the heating uidhaving a gradually increasing temperature dilerential therebetweenupwardly of the heating section.

Since the shaft kiln is The-lowermost of the annular chambers 62receives a portion of the heating gases passing upwardly through thekiln and directs the by-passed gas through the flow control orifice inthe cap e4'. The upper annular chamber E2 also receives a `portion ofthe heating gases, which will be at a somewhat lower temperature, anddischarges the by-passed gas to the atmosphere. In eifect, the verticalspacing of the two annular chambersA 62 provides a transition Zone ofpellet heating between the sections l2 and l l, where the gas flowthrough the in-terstices of the pellet mass is lowered in two steps, toreduce the abruptness of change in heat transfer rate between theadjacent heating ,andV preheating section. ThisA is advantageous inpellet heating, when the amount of ley-passed gas may be equal to asmuch as 50 percent of the total volume of gas introduced at the lowerend or" the heating section. The number and vertically spacedrelationship of the annular chambers 62 will depend primarily upon theamount of heating fluid by-passed. Under some conditions, only oneannular oy-pass chamber will be sufficient for the contemplated heatinggas flows. Under other conditions it will be desirable to provide threeor even more vertically spaced by-pas's outlets for the partially spentgaseous heating fluid.

By way of example and not of limitation a shaft kiln of the typedisclosed and of the illustrated general proportions, has been operatedat a i'low rate of 170 pounds of the described pellets per hour. Thekiln sections l, I2 and i3 were constructed with an internal diameter ofapproximately 9 inches, while the internal opening of the tubular member55 was approximately 41/2 inches. Under these conditions and at asubstantially' uniform rate of pellet movement, individual pelletsremained in the kiln approximately 4 hours in moving through thesuccessive sections of the kiln. The pellets attained a temperature ofapproximately 3000 F. with a heating gas temperature of 3000 F., and agas flow rate of 290 pounds per hour. The lowermost annular by-passchamber 62 withdrew by-passed heating gas at a temperature ofapproximately 2270 F., While the upper chamber 62 withdrew by-passedheating gas having a temperature of approximately 1700 F. The quantityof by-passed gaseous heating fluid totaled approximately pounds perhour. With the pellets described the ytheoretical gas flow rate wouldbeof the order of pounds per hour and while the thermal eiciency of theunit would be high, without the use of heating gas by-passes, thefinished product would not be uniform, and thus would be unsatisfactoryfor the pellet end VUSE.

It will be noted that the present invention provides for a flow ofheating gases into a gaspervious mass of fluent solid material undertemperature and flow rate conditions causing the solid material toattain a substantially uniform temperature transversely of the movingmass in the region of .highest material temperatures. A portion of theheating gases are withdrawn from the heating zone of the shaft kilnafter giving up a part of their sensible heat to the fluent solidmaterial. The heating gases are produced by the combustion of a fuel ina furnace with a measured part of the combustion air preheated incooling the finished product within thelower portion cf the kiln. Theheating gases not-only heat the mass of solid material by direct contactheat exchange in the upper portion of the kiln, but also heat thematerial in an intermediate portion of the kiln by conduction andconvection. Since the preheated air contains dust entrained in itspassage through lthe finished material, a substantial portion ofparticularly the larger particles of dust are advantageously removedbefore mixing with the fuel and other air for combustionpurposes. Thisreduces the tendency for dust to accumulate in the apparatus and to plugor restrict the heating gas flow passages.

While in accordance with the provisions of the statutes 'I haveillustrated and described herein the best' form and mode of Aoperationof the in- Vention now known to me, those skilled in the art willunderstand that changes may be made in the form of the apparatusdisclosed without departing from the spirit of the invention covered bymy claims, and that certain features of my invention may sometimes beused to advantage without a corresponding use of other features.

I claim:

1. The method of continuously heating a moving mass of fluent solidmaterial at a normal operating rate and to a high temperature whichcomprises introducing a gas heated to a high temperature into saidmoving mass in a heating zone in a Weight 50 to 100% in excess of thetheoretical heat requirements to heat the mass of material to asubstantially uniform temperaturentransversely of the moving mass andsubstantially equal to the temperature of the entering heating gas,passing said heating gas in countercurrent flow through the intersticesof said moving mass, discharging a portion of said heating gas generallyequal in weight to said excess of heating gas from said heating zone toatmosphere,

'and utilizing the remaining portion of said heating gas to preheat saidmoving mass.

2. The method of continuously heating a downwardly moving mass of fluentsolid material at a quirement to heat the mass of fluent solid ma-Aterial and at a temperature substantially equal to the desired fluentsolid material temperature, heating said mass at a high rate oftemperature rise in an intermediate portion of said heating zone,discharging a portion vof the partially cooled I heating gas from thelower region of the intermediate portion of said zone to atmosphere, andreducing the high rate of temperature rise in said mass in theintermediate portion of said heating zone by discharging to atmosphere afurther portion of the further partially cooled heating gas from theupper region of said intermediate zone.

3. The process of vitrifying ceramic particle materials which comprisespassing a fluent mass 75' of said ceramic particle materials downwardlyat a generally uniform rate through heating, soaking and cooling zones,heating the material within said heating zone by direct contactcountercurrent heat transfer relationship with a heating fluid having aheat content approximately 5G to 100% in excess of the theoretical heatrequirements and being at a temperature substantially equal to thedesired ceramic particle temperature, withdrawing and discharging toatmos- 'I phere a substantial portion of said heating fluid from theheating zone after said fluid has given up a part of its sensible heatto said ceramic material, utilizing the remainder of said heating fluidto preheat the ceramic material in the remaining portion of said heatingzone, soaking said ceramic material at a high temperature within saidsoaking zone substantially out of direct contact with any fluid tocomplete vitrication of said material, cooling said material by directcontact countercurrent relationship with a measured stream of coolingair having a weight generally equal to the air weight necessary tocombine with fuel to generate the heating fluid theoretically necessaryto heat the ceramic particle materials in said heating zone, andcombining the heated cooling air from said material cooling zone with ameasured mixture of gaseous fuel and air in a separate combustion zoneto generate said heating fluid.

4. Apparatus for the heat treatment of a fluent mass of solid materialcomprising walls defining an elongated shaft kiln having an upper inletand a lower outlet for said fluent solid material, means for causing acontinuous movement of said material through said kiln, a combustionchamber enclosed within the wall of an intermediate portion of said kilnand in communication with the interior of said kiln at an upperintermediate position, a subjacent chamber in communication with saidcombustion chamber and with said kiln at a lower intermediate position,a burner arranged to deliver a mixture of fuel and combustion air tosaid combustion chamber, means for preheating a portion of thecombustion air by heat exchange in cooling said heat treated fluentsolid material, and means for removing at least the larger particles ofdust from said preheated combustion air in said subjacent chamber.

5. Apparatus for the heat treatment of a fluent mass of solid materialcomprising walls defining an elongated shaft kiln having an upper inletand a lower outlet for said fluent solid material, means for causing acontinuous movement of said material through said kiln, a combustionchamber enclosed within the wall of an intermediate portion of said kilnand in communication with the interior of said kiln at an upperintermediate position, a subjacent chamber in communication with saidcombustion chamber and with said kiln at a lower intermediate position,a burner arranged to deliver a mixture of fuel and combustion air tosaid combustion chamber, said burner having an annular jacket radiallyspaced from and enclosing the tip of said burner and having an exteriorwater inlet connection at the bottom of said jacket and a water outletpipe connected into the upper end of said jacket, said water outlet pipeextending longitudinally of the interior of said burner to an exteriorposition, and means for introducing another portion of the air forcombustion into said subjacent chamber in a preheated condition and in atangential direction adjacent the discharge end of said burner.

6. Apparatus for the heat treatment f a fluent mass of solid materialcomprising walls defining a vertically elongated kiln having a solidmaterial inlet and a heating gas outlet at its upper end and a solidmaterial outlet at its lower end, means for causing a downward movementof said solid material as a continuous column through said kiln, saidkiln having a soaking zone intermediate its height including a portionof reduced crosssection, a vertically elongated furnace chamber embeddedin the wall of said kiln and having its l1 upper end opening to saidkiln at the upper end of said soaking zone, a lower vertically elongatedchamber embedded in the wall of said kiln and in communication with saidfurnace through a connecting throat, said lower chamber having atangentially arranged inlet in the upper end thereof for the admissionof preheated air from the lower portion of said kiln, a fuel burnerarranged to discharge a mixture of fluid fuel and another portion of thecombustion air axially into the lower end of the throat between saidlower chamber and furnace chamber, and means for withdrawing anddischarging to atmosphere a portion of the heating gases from said kilnchamber at a location intermediate the upper end 15 opening of saidfurnace chamber into said kiln and said kiln heating gas outlet.

PAUL R. GROSSMAN.

REFERENCES CITED The following'references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 1,175,247 Doherty Mar. 14, 19161,798,802 Niles Mar. 31, 1931 2,115,586 McFarland Apr. 26, 19382,199,384 Azbe May 7, 1940 2,370,281 Azbe Feb. 27, 1945

